C++ (Qt)
void reformatSpan( QTextDocument& doc, int pos, int length, const QTextCharFormat& format )
{
	QTextCursor cursor(&doc);
	cursor.setPosition(pos, QTextCursor::MoveAnchor);
	cursor.setPosition(pos + length, QTextCursor::KeepAnchor);
	cursor.mergeCharFormat(format);
}